Facile synthesis and excellent electrochemical properties of NiCo2O4 spinel nanowire arrays as a bifunctional catalyst for the oxygen reduction and evolution reaction

Developing catalysts with high electrocatalytic activity for an oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) has recently attracted much attention because the sluggish kinetics of these two reactions limits the performance and commercialization of fuel cells and metal-air batteries. Herein, a facile template-free co-precipitation route was reported for the design and fabrication of well-ordered NiCo2O4 (NCO) spinel nanowire arrays. The as-prepared NCO spinel nanowire arrays are characterized by XRD, SEM, TEM, BET and XPS. BET results show that NCO spinel nanowire arrays have a mesoporous (ca. 8 nm) structure and a high specific surface area of 124 m(2) g(-1). The catalytic activity of NCO spinel nanowire arrays for the ORR and the OER in 0.1 M KOH solution has been studied by using a rotating ring-disk electrode (RRDE) technique. RRDE results show that the NCO spinel nanowire array catalyst exhibits excellent catalytic activity for the ORR. The ORR mainly favors a direct four electron pathway, which is close to the behavior of the Pt/C (20 wt% Pt on carbon) electrocatalyst under the same testing conditions. Anodic linear scanning voltammogram results show that the NCO spinel nanowire array catalyst is more active for the OER. The chronoamperometric and cyclic voltammogram tests show that the NCO spinel nanowire array catalyst exhibits excellent stability and reversibility for the ORR and the OER.